Synthesis and photolysis of hexahydropyrrolo[3,4-c]pyrazole derivatives

Article abstract of DOI:10.3184/030823407X255515

The 1,3-dipolar cycloaddition of 2-diazopropane 1 with N-arylcitraconimides and N-arylmaleimides 2, at -78°C, has led to monoadducts 3. The same addition of 2-diazopropane with maleimide 4, has led to a new and unexpected Δ³-1,3,4-oxadiazoline

Full text of DOI:10.3184/030823407X255515

JOURNAL OF CHEMICAL RESEARCH 2007
OCTObER, 569–571
RESEARCH PAPER 569
Synthesis and photolysis of hexahydropyrrolo[3,4-c]pyrazole derivatives
Naoufel Ben Hamadi*, Nesrine Louhichi and Moncef Msaddek
Laboratoire de Synthèse Hétérocyclique et Substances Naturelles, Département de Chimie, Faculté des Sciences 5000 Monastir,
Tunisie
The 1,3-dipolar cycloaddition of 2-diazopropane 1 with N-arylcitraconimides and N-arylmaleimides 2, at –78°C, has
led to monoadducts 3. The same addition of 2-diazopropane with maleimide 4, has led to a new and unexpected D3-
1,3,4-oxadiazoline 5. Irradiation of the pyrazolines 3 led to clean extruction of nitrogen to give the cyclopropanes 6.
Keywords: 1,3-cycloaddition, D1-pyrazolines, oxadiazoline, cyclopropanes
One of the most important reactions for the construction of five-
membered heterocyclic rings is the 1,3-dipolar cycloaddition
reaction.1-4 The chemical reactivity of diazoalkanes according
to alkenes,5,6 as well as the regio- and the stereoselectivity of
theses reactions have been thoroughly studied. Considerable
attention has been focused on the synthesis of pyrazolines,7
bothfortheirhighpharmacologicalandbiologicalactivities.8-13
in dichloromethane at –78°C leads to the corresponding D1-
pyrazolines 3 in good yield (Scheme 1).
The H NMR spectra of the adducts are consistent with
1
the structure assignments shown in Scheme 1, which are
compatible with the direction of bond polarisation of both
reactants. The cis relationship of the two rings in all adducts
is supported by the coupling constant of 8.3 Hz observable
between H3a and H6a. In all cases, only one regioisomeric
pyrazolineswasobtained,indicatinghighregioselectivityofthe
transformation. We now have to determine the addition mode
of 2-diazopropane with N-arylcitraconimides. Unambiguous
proofs for the obtained cycloadducts regiochemestry arised
from their spectral data. However, regiochemical assignments
of all adduct were deduced from their 13C NMR spectra.
Particularly the chemical shifts of C6a (99.91–100.30 ppm)
are in excellent agreement with those usually obtained when
this quaternary carbon is attached to nitrogen atom.19
Cyclopropane ring,
a common motif among natural
compounds, deserves high interest, in terms of access,
synthetic potential, and bioactivities.14-16 In continuation
to our work on the synthesis of heterocycles via 1,3-dipolar
cycloaddition and evolution of cycloadducts,17,18 we reported
previously the development of 1,3-dipolar cycloaddition of
2-diazopropane. We now describe how these compounds can
be converted to cyclopropanes.
Results and discussion
1,3-dipolar cycloaddition of ethereal 2-diazopropane 1 to a
solution of N-arylcitraconimides 2 and N-arylmaleimides 2
On the other hand, the same reaction is carried out under
similar operating conditions with maleimide 4, has led to a
R2
O
O
R2
N
H3C
Et2O, –78°C
6
4
1
6a
3a
R1
N
O
R1
N
N
N
N
5
2
3
H3C
H
1
H
H3C
O
CH3
2
3
a: R1= H, R2 = H
b: R1= H, R2 = CH3
c: R = OCH3, R2 = H
1
d: R1= OCH3, R2 = CH3
e: R = NO2, R2 = H
1
f: R = NO2, R2= CH3
1
Scheme 1
H3C
CH3
c
d
N
N
5'
2'
4'
3'
O
1'
O
H
N
H3C
H3C
6
1
Et2O, -78°C
6a
3a
N
O
H
N
N
5
2
N
N
H
2
3
4
H
H3C
a
O
CH3
b
4
5
Scheme 2
* Correspondent. E-mail : bh_naoufel@yahoo.fr
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570 JOURNAL OF CHEMICAL RESEARCH 2007
R2
O
R2
O
N
H3C
H3C
2
4
hn
1
5
R1
N
N
R1
6
3
N
-N2
H3C
CH3
O
O
6
3
a: R 1= H, R2= H
b: R 1= H, R2= CH3
c: R1= OCH 3, R2= H
d: R 1= OCH 3, R2= CH3
e: R1= NO2, R2= H
f: R1= NO2, R2= CH3
Scheme 3
(dichloromethane–ether of petrol). MS, m/z (%): [M+.-N2, 215], 215
(100%). Anal. Calcd. for C13H13N3O2: C, 64.19; H, 5.39; N, 17.27%;
Found: C, 65.10; H, 5.35; N, 17.17%; IR ncm-1; 1518 (N=N); 1680,
new and unexpected heterocyclic structure 5. Microanalyses
indicate that 5 result from addition of two DAP equivalent.
On the other hand, H NMR spectra of adduct 4 shows four
1
1
1670 (C=O). H NMR (300 MHz; CDCl3) dppm: 1.58 (s, 3H, CH3),
methyl singlets (Scheme 2).
1.64 (s, 3H, CH3), 3,00 (d, 1H, H3a), 5.99 (d, 1H, H6a): AX patt.
JH3a-H6a = 8.3 Hz, 7.21–7.51 (m, 5H, Harom). 13C NMR (75 MHz;
The chemoselectivity of the addition of 2-diazopropane
with the carbonyl function was deduced from their HMbC 2D
NMR spectra. The methyl protons Ha and Hb correlate with
CDCl3) dppm: 22.94 (CH3), 28.25 (CH3), 47.40 (C3a), 94.24
(C3), 95.39 (C6a), 125.18–131.23 (Carom), 168.77 (C4), 173.21 (C6).
3,3,6a-trimethyl-5-phenyl-3,3a,4,5,6,6a-hexahydropyrrolo[3,4-c]
pyrazole (3b): White crystals (1.25 g, 91%), m.p. 98°C, MS, m/z (%):
[M+.-N2, 229], 229 (100%). Anal. Calcd. For C14H15N3O2: C, 65.34;
H, 5.89; N, 16.33%; Found: C, 65.50; H, 5.80; N, 16.45%; IR (Kbr)
ncm-1; 1510 (N=N); 1725, 1730 (C=O). 1H NMR (300 MHz, CDCl3)
d: 1.52 (s, 6H, CH3), 1.83 (s, 3H, CH3), 2.58 (s, 1H, H3a), 7.14–7.41
(m, 5H, Harom); 13C NMR (75 MHz, CDCl3) d: 20.88 and 23.19
(CH3), 29.06 (CH3), 53.34 (C3a), 95.45 (C3), 100.30 (C6a), 126.61–
131.41 (Carom), 172.15 (C4), 172.84 (C6).
3
carbons atom C3a (47.23 ppm), C4 (172.41 ppm) via J and
4J coupling constants.
Regiochemistry of oxadiazoline 5 could be also established
from their 13C spectra. The high chemical shifts of C6
(149.90 ppm) and C5’ (130.16 ppm) indicate that each of
these two carbons is linked to heteroatoms. The “inverse”
regiochemical sense in cycloaddition of 2-diazopropane on
the carbonyl function seems to be essentially conditioned by
steric factors.
3,3-dimethyl-5-(4-methoxyphenyl)-3,3a,4,5,6,6a-hexahydro-
pyrrolo[3,4-c]pyrazole (3c): White crystals (1.17 g, 80%),
m.p. 103°C (dichloromethane–ether of petrole). MS, m/z (%):
The photolysis of an ethereal solution of the D1-pyrazolines
3 through Pyrex with a high pressure mercury arc lamp
(Philips HPK 125 W) at 0–5°C led to exclusive formation of
gem-dimethylcyclopropanes 6 (Scheme 3).20
Thisstudydemonstratesthatthegem-dimethylcyclopropanes
subunit which is often incorporated into biologically important
natural products can easily be obtained in a two-step sequence
from N-arylcitraconimides and N-arylmaleimides. During the
1,3-dipolar cycloaddition of 2-diazopropane with maleimide
derivatives, both carbonyl and ethylenic double bond can be a
priori, subjected to 1,3-dipolar attack.
[M+.-N2, 245], 96 (100%). Anal. Calcd. For C14H15N3O3: C, 61.52;
-1
H, 5.54; N, 15.37%; Found: C, 62.01; H, 5.45; N, 13.41%; IR ncm
;
:
1
1526 (N=N); 1695, 1700 (C=O). H NMR (300 MHz; CDCl3) dppm
1.57 (s, 3H, CH3), 1.62 (s, 3H, CH3), 2.98 (d, 1H, H3a), 5.97 (d, 1H,
H6a): AX patt. JH3a-H6a = 8.3 Hz, 3.83 (s, 3H, OCH3), 6.96 (d, 2H) and
7.11 (d, 2H): AA'bb' patt. J = 8.4 Hz; 13C NMR (75 MHz; CDCl3)
d
ppm: 22.94 (CH3), 28.24 (CH3), 47.34 (C3a), 55.93 (OCH3), 94.22
(C3), 95.25 (C6a), 115.00–160.19 (Carom), 169.04 (C4), 173.47 (C6).
3,3,6a-trimethyl-5-(4-methoxyphenyl)-3,3a,4,5,6,6a-
hexahydropyrrolo[3,4-c]pyrazole (3d): White crystals (1.23 g, 80%),
m.p. 140°C, MS, m/z (%): [M+.-N2, 259], 134 (100%). Anal. Calcd.
For C15H17N3O3: C, 62.69; H, 5.97; N, 14.63%; Found: C, 62.73; H,
5.99; N, 14.49%; IR (Kbr) ncm-1; 1516 (N=N), 1720, 1738 (C=O).
1H NMR (300 MHz, CDCl3) d: 1.51 (s, 6H, CH3), 1.82 (s, 3H, CH3),
2.61 (s, 1H, H3a), 3.75 (s, 3H, OCH3), 6.87 (d, 2H) and 7.05 (d, 2H):
AA'bb' patt. J = 9 Hz; 13C NMR (75 MHz, CDCl3) d: 20.88 and
23.18 (CH3), 29.04 (CH3), 53.27 (C3a), 55.91 (OCH3), 95.32 (C3),
100.27 (C6a), 114.94–160.13 (Carom), 172.38 (C4), 173.09 (C6).
3,3-dimethyl-5-(4-nitrophenyl)-3,3a,4,5,6,6a-hexahydro-
pyrrolo[3,4-c]pyrazole (3e): Yellow crystals (1.08 g, 70%),
m.p. 130°C, MS, m/z (%): [M+.-N2, 260], 260 (100%). Anal. Calcd.
For C13H12N4O4: C, 54.17; H, 4.20; N, 19.44%; Found: C, 54.62; H,
4.25; N, 19.45%; IR (Kbr) ncm-1; 1520 (N=N), 1689, 1695 (C=O).
1H NMR (300 MHz, CDCl3) d: 1.63 (s, 6H, CH3), 2,90 (d, 1H, H3a),
6.01 (d, 1H, H6a), AX patt. JH3a-H6a = 8.3 Hz, 7.56 (d, 2H) and 8.42
(d, 2H): AA'bb' patt. J = 9 Hz; 13C NMR (75 MHz, CDCl3) d: 21.45
and 22.87 (CH3), 54.62 (C3a), 94.35 (C3), 95.98 (C6a), 123.47–146.10
(Carom), 172.16 (C4), 173.02 (C6).
Experimental
Generalities: IR spectra were recorder on Perkin-Elmer IR-197
IR spectrometer. Mass spectra were determined on a Nierjohnson
MS80RF spectrometer. Melting points were determined on a buchi-
510 capillary melting point apparatus. Thin layer chromatography
(TLC) was performed on silica gel 254 plates (Merck) with UV
(254 nm) visualisation whereas chromatographic separations were
conducted on silica gel Si-60-7734 Merck using water-Jacketed
columns. 1H NMR and 13C NMR spectra recorded at 300 MHz
and 75.47 MHz, respectively. Coupling constants are given in
Hz. Elemental analyses were performed on a Perkin-Elmer 240b
microanalyser. Diethyl ether was freshly distilled over sodium wire
with a trace of benzophenone. Dichloromethane was distilled from
calcium hydride.
3,3,6a-trimethyl-5-(4-nitrophenyl)-3,3a,4,5,6,6a-hexahydro-
pyrrolo[3,4-c]pyrazole (3f): Yellow crystals (1.52 g, 94%),
m.p. 147°C, MS, m/z (%): [M+.-N2, 274], 274 (100%). Anal. Calcd.
For C14H14N4O4: C, 55.65; H, 4.67; N, 18.52%; Found: C, 55.45; H,
4.62; N, 18.65%; IR (Kbr) ncm-1; 1520 (N=N), 1718, 1735 (C=O).
1H NMR (300 MHz, CDCl3) d: 1.60 (s, 6H, CH3), 1.92 (s, 3H, CH3),
2.71 (s, 1H, H3a), 7.53 (d, 2H) and 8.31 (d, 2H): AA'bb' patt. J = 9 Hz;
13C NMR (75 MHz, CDCl3) d: 20.45 and 22.86 (CH3), 28.65 (CH3),
52.92 (C3a), 95.67 (C3), 99.91 (C6a), 124.53–147.00 (Carom), 171.06
(C4), 171.07 (C6).
General procedure for trapping of 2-diazopropane with
N-arylmaleimides and N-arylcitraconimides
To a stirred solution containing 5.34 mmol of 2 or 4 in 50 ml of
anhydrous dichloromethane at –78°C was added in small fractions a
2.6M ethereal solution prepared at –78°C. The progress of the reaction
was monitored by TLC control (60–40 hexane-ethyl acetate elution)
and the reaction was discontinued when 2 or 4 had totally reacted.
The solution was allowed to react 6 h at 0°C and the solvent was
evaporated under reduced pressure. Recrystallisation from ethanol.
3,3-dimethyl-5-phenyl-3,3a,4,5,6,6a-hexahydropyrrolo[3,4-c]
pyrazole (3a): White crystals (1.16 g, 90%), m.p. 136°C
3,3,5',5'-tetramethyl-3a,4,5,6a-tetrahydro-3H,5'H-spiro[pyrrolo
[3,4-c]pyrazole-6,2'-[1,3,4]oxadiazole]-4-one (5): White solid
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JOURNAL OF CHEMICAL RESEARCH 2007 571
(0.82 g, 65%), m.p. 114°C, MS, m/z (%): [M+., 237], 209 (100%).
Anal. Calcd. For C10H15N5O2: C, 50.62; H, 6.37; N, 29.52%; Found:
C, 50.49; H, 6.31; N, 29.43%; IR (Kbr) ncm-1; 1540 (N=N), 1720,
was irradiated as previously described to give a yellow solid. Yield
75%, m.p. = 147°C, MS, m/z (%): [M+., 274], 274 (100%). Anal.
Calcd. For C13H12N2O4: C, 60.00; H, 4.65; N, 10.76%; Found: C,
1
(C=O). H NMR (300 MHz, CDCl3) d: 1.45; 1.59 (s, 3H, CH3(a,b)),
1
60.05; H, 4.70; N, 10.62%; H NMR (300 MHz, CDCl3) d: 1.14 (s,
2.02; 2.14 (s, 3H, CH3(c,d)), 2.76 (s, 1H, H3a), 5.91 (s, 1H, H6a),
AX patt. JH3a-H6a = 8.4 Hz, 8.93 (s, 1H, NH); 13C NMR (75 MHz,
CDCl3) d: 18.72, 22.36, 25.22 and 22.86 (CH3), 27.77 (CH3), 47.23
(C3a), 91.67 (C3), 93.82 (C6a), 130.16 (C5’), 149.90 (C6), 172.41 (C4).
3H, CH3), 1.23 (s, 3H, CH3), 2.35 (s, 2H, H1,5), 7.39 (d, 2H) and 8.09
(d, 2H): AA'bb' patt. J = 9 Hz; 13C NMR (75 MHz, CDCl3) d: 9.31
and 17.18 (CH3), 36.13 (C1), 36.70 (C5), 36.81 (C6), 122.42–146.38
(Carom), 171.47 (C4), 173.99 (C2).
General procedure for the irradiation of the D1-pyrazolines (3)
All irradiation were carried out using similar conditions.
The derivative was dissolved in ether (pre-treated by stirring with
solid (NaCO3), filtering and flushing with argon) and irradiation at
5°C for a total of 2 hours or until the starting materiel was consumed
(TLC). After this period the solvent was removed in a vacuum
without heating to give brown oil, which was subjected to rapid silica
filtration. Recrystallisation from light petroleum.
1,6,6-trimethyl-3-(p-nitrophenyl)-3-azabicyclo[3.1.0]hexane-2,4-
dione (6f): A solution of 3f (500 mg, 1.65 mmol) in ether (200 ml)
was irradiated as previously described to give a yellow solid. Yield
75%, m.p. = 158°C, MS, m/z (%): [M+., 274], 274 (100%). Anal.
Calcd. For C14H14N2O4: C, 61.31; H, 5.14; N, 10.21%; Found: C,
1
61.19; H, 5.40; N, 10.31%; H NMR (300 MHz, CDCl3) d: 1.27 (s,
3H, CH3), 1.29 (s, 3H, CH3), 1.52 (s, 3H, CH3), 2.15 (s, 1H, H5), 7.49
(d, 2H) and 8.22 (d, 2H): AA'bb' patt. J = 9 Hz; 13C NMR (75 MHz,
CDCl3) d: 9.19 and 16.17 (CH3), 21.97 (CH3), 36.03 (C1), 36.69 (C5),
36.79 (C6), 123.32–145.52 (Carom), 171.51 (C4), 174.51 (C2).
6,6-dimethyl-3-phenyl-3-azabicyclo[3.1.0]hexane-2,4-dione
(6a): A solution of 3a (500 mg, 1.95 mmol) in ether (200 ml) was
irradiated as previously described to give a white solid. Yield 50%,
m.p. = 123°C, MS, m/z (%): [M+., 215], 215 (100%). Anal. Calcd.
For C13H13NO2: C, 72.52; H, 6.10; N, 6.51%; Found: C, 72.60; H,
Received 12 July 2007; accepted 16 October 2007
Paper 07/4743 doi: 10.3184/030823407X255515
1
6.02; N, 6.39%; H NMR (300 MHz; CDCl3) d: 1.30 (s, 3H, CH3),
1.41 (s, 3H, CH3), 2.48 (s, 2H, H1,5), 7.24–7.46 (m, 5H, Harom); 13C
NMR (75 MHz; CDCl3) d: 16.01 (CH3), 25.74 (CH3), 33.70 (C1,5),
35.39 (C6), 126.28–131.54 (Carom), 172.92 (C2,4).
References
1,6,6-trimethyl-3-phenyl-3-azabicyclo[3.1.0]hexane-2,4-dione
(6b): A solution of 3b (500 mg, 1.95 mmol) in ether (200 ml) was
irradiated as previously described to give a white solid. Yield 70%,
m.p. = 118°C, MS, m/z (%): [M+., 229], 110 (100%). Anal. Calcd.
For C14H15NO2: C, 73.36; H, 6.60; N, 6.10%; Found: C, 73.60; H,
1
2
E. buchner, Ber. Dtsch. Chem. Ges., 1888, 21, 2637.
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3
4
5
1
6.39; N, 6.30%; H NMR (300 MHz, CDCl3) d: 1.30 (s, 3H, CH3),
1.38 (s, 3H, CH3), 1.56 (s, 3H, CH3), 2.16 (s, 1H, H5), 7.28–7.47 (s,
5H, Harom); 13C NMR (75 MHz, CDCl3) d: 10.28 and 17.18 (CH3),
23.05 (CH3), 36.77 (C1), 37.62 (C5,6), 126.18–131.64 (Carom), 173.53
(C4), 176.35 (C2).
6
7
3-anisyl-6,6-dimethyl-3-azabicyclo[3.1.0]hexane-2,4-dione (6c):
A solution of 3c (500 mg, 1.95 mmol) in ether (200 ml) was
irradiated as previously described to give a white solid. Yield 60%,
m.p. = 113°C, MS, m/z (%): [M+., 215], 215 (100%). Anal. Calcd.
For C14H15NO3: C, 68.56; H, 6.16; N, 5.71%; Found: C, 68.63; H,
8
9
M. berghot and E. Moaward, Eur. J. Pharm. Sci., 2003, 20, 173.
1
6.20; N, 5.79%; H NMR (300 MHz; CDCl3) d: 1.29 (s, 3H, CH3),
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1.36 (s, 3H, CH3), 2.44 (s, 2H, H1,5), 3.84 (s, 3H, OCH3), 6.88
(d, 2H) and 7.17 (d, 2H): AA'bb' patt. J = 8.4 Hz; 13C NMR
(75 MHz; CDCl3) d: 16.31 (CH3), 25.54 (CH3), 32.71 (C1,5), 36.31
(C6), 56.03 (OCH3), 115.10–161.09 (Carom), 171.82 (C2,4).
3-anisyl-1,6,6-trimethyl-3-azabicyclo[3.1.0]hexane-2,4-dione
(6d): A solution of 3d (500 mg, 1.74 mmol) in ether (200 ml) was
irradiated as previously described to give a yellow solid. Yield 65%,
m.p. = 138°C, MS, m/z (%):[M+., 259], 67 (100%). Anal. Calcd.
For C15H17NO3: C, 69.46; H, 6.62; N, 5.40%; Found: C, 69.37; H,
16 C. Cativiela and D. Diaz-de-Viellgus, Tetrahedron Asymmetry, 2000,
11, 645.
1
6.80; N, 5.29%; H NMR (300 MHz, CDCl3) d: 1.29 (s, 3H, CH3),
1.37 (s, 3H, CH3), 1.55 (s, 3H, CH3), 2.13 (s, 1H, H5), 3.80 (s, 3H,
OCH3), 6.93 (d, 2H) and 7.16 (d, 2H): AA'bb' patt. J = 9 Hz; 13C
NMR (75 MHz, CDCl3) d: 10.28 and 17.18 (CH3), 23.04 (CH3),
36.69 (C1), 37.55 (C5), 37.61 (C6), 55.53 (OCH3), 114.46–159.27
(Carom), 173.84 (C4), 176.62 (C2).
6,6-dimethyl-3-(p-nitrophenyl)-3-azabicyclo[3.1.0]hexane-2,4-
dione (6e): A solution of 3e (500 mg, 1.65 mmol) in ether (200 ml)
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